The invention relates to a method and apparatus for measuring a physical quantity, property or condition, transmitting a code representing the physical property, quantity or condition to a receiver and displaying a representation of the physical property, quantity or condition on a display at a central location. Such an apparatus and method has particular application in monitoring pressures and temperatures of air in tires, and displaying such air pressures and temperatures on a display located in a cab portion of a vehicle on which the apparatus is installed.
In pneumatic tired vehicles such as mining trucks, logging trucks, and semi-trailers etc, pneumatic tire problems can affect the operating cost of such vehicles. Operating costs are affected when a tire becomes flat due to wear or puncture as tires must often be replaced or repaired. This leads not only to a cost in affecting the repair but also leads to a cost due to temporary loss of use of the vehicle.
Other problems associated with pneumatic tires include road wear due to improperly inflated tires and loss of effectiveness of anti-lock breaking systems resulting from reduced friction due to over or under inflation of tires.
Operating costs of vehicles can, however, be minimized and road wear and loss of effectiveness of anti-lock breaking systems can be reduced by careful maintenance of tires. More specifically, if tire pressures are monitored and maintained within pre-defined limits, tire wear and road wear can be reduced and the effectiveness of anti-lock breaking systems can be maintained. Additionally, if the air temperature within a tire is monitored, excessive heating of the tire can be observed, serving as a warning that possible tire damage or blowout is imminent.
Previously, monitoring of tire pressures and temperatures was done by simply using a conventional tire gauge to measure tire pressure and by simply touching the tire to determine if it appeared excessively warm. While the use of the pressure gauge is reasonably accurate, it could only be used while the vehicle was stopped. Measuring temperature also had to be done while the vehicle was stopped and an operator could only guess that the tire may be too hot.
What is required therefore is a method and apparatus for monitoring tire pressures and temperatures while the vehicle is in use.
Certain inventors before us have sought to address the problem of measuring tire pressure. For example the U.S. Pat. No 4,237,728 to Betts et al. discloses a low tire warning system which monitors tire inflation and sends a coded signal to a central receiver when the tire inflation is less than a predetermined value or threshold. It appears that actual tire pressure is not monitored, but instead a warning is generated when threshold is attained. Furthermore, there appears to be no mention of measurement of air temperature within the tire.
U.S. Pat. No. 4,742,857 to Gandhi discloses a tire pressure sensor and air supply for maintaining a desired air pressure in a tire. The device monitors air pressure in a tire by creating movement of a reluctance-type of pressure sensing element which cooperates with a receiving transducer mounted adjacent the tire, on the frame of the vehicle. While continuous measurement of tire pressure is possible, installation of a plurality of reluctance sensor elements and corresponding transducers is required. Furthermore, the transducers must be placed in close proximity to the sensor elements on the tires resulting in little clearance between the sensor and transducer. This can leave the system susceptible to damage due to debris lifted from the road by a tire as could frequently occur if the device was used with a mining vehicle or logging truck. Furthermore, Gandhi does not appear to disclose simultaneous monitoring of air temperature within a tire.
U.S. Pat. No. 4,067,235 to Markland et al. discloses a method and apparatus for measuring air in pneumatic tires. The system involves the use of first and second coils embedded in a portion of roadway over which the vehicle is driven and stopped upon. The first coil excites a primary receiving coil of a transducer embedded within the tire and thereby provides power to the transducer. The transducer then measures the air pressure in the tire and produces an output signal which has a frequency proportional to air pressure in the tire. This output signal is received by the second coil in the roadway which is connected to a monitoring apparatus beside the roadway. There is no mention that the device may be modified to permit monitoring of tire pressure and temperature while the vehicle is in use.
The present invention seeks to solve the problem of monitoring tire pressure and temperature while the vehicle is in use.